We investigated on the interaction between a single guided-mode resonance and Fabry-Perot resonance (FPR) in a high contrast grating (HCG) from a viewpoint of Fano resonance. It has been found that the background reflection due to the FPR in the HCG is useful to implement flat-top broadband reflectors via tailoring the phase polarity of Fano resonance. The novel conceptual approach was elucidated theoretically with the temporal coupled-mode theory (TCMT), which was confirmed by the Si HCG broadband reflector design of 380-nm bandwidth for R > 99.9 from 1400 to 1780 nm (a fractional bandwidth of 24.5%). The TCMT model was in good agreement with the rigorous coupled wave analysis calculation. We believe that our approach provides expanded understanding on Fano resonance in a grating, enabling more intuitive and simpler design of a flat-top broadband reflector with grating structures.
Manuscript received March 13, 2019; revised June 6, 2019; accepted June 7, 2019. Date of publication June 12, 2019; date of current version August 8, 2019. This work was supported by the National Research Fund of Korea (NRF-2017R1A2A2A05001226). (Corresponding author: Sangin Kim.) The authors are with the Department of Electrical and Computer Engineering, Ajou University, Suwon 16499, South Korea. (e-mail: bluesky525@ajou.ac.kr; lsjkmjh@ajou.ac.kr; sangin@ajou.ac.kr).
